Journal of Research of the National Bureau of Standards
AbstractThe standard pH values of the solution of potassium hydrogen phthalate (molality 0.05 mol kg- 1) have been redetermined over the temperature range 0 to 60 �C, using SRM 185d. Extensive measurements were made of the emf of cells of the type Pd; H2(g, 1 atm)|KH phthalate (m = 0.05), KCI (m)|AgCI;Ag where mKCI was 0.015, 0.01, or 0.005 mol kg-1, from which values of the acidity function p(aHYc1) were derived. The pH convention defines Yc1 in the range of ionic strengths 0 to 0 .1 mol kg- 1 and permits conventional values of paH to be obtained. According to NBS procedures, paH for selected reference solutions is identified wilh the standard pH(S) in the operational definition or pH. The new values, given in terms or the thermodynamic temperature (T) by 2073.44 pH(S) = --T- - 13.3270 + 0.045199T - 3.4846 X 5T2 differ, on the average, by 0.003 unit from the results based on the 1944 data of Hamer and Acree.
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